In the matter of stirring liquids by apparatus in lieu of hand-stirring, the attempt has always been to obtain circulation of the liquid composition within the container. The greater degree of circulation results in improved intermingling and homogenizing of the composition or better dispersion of particles within the liquid. In many instances, heat must be applied to the container in addition to he stirring action to achieve the desired results. In other instances, such as certain laboratory work, heating must be avoided, be it from external sources or as can be developed by the very motion and operation of the stirring apparatus.
The path to be followed by the stirrer can enhance the stirring if the proper motion is imparted to the stirrer. In contrast, stirring will be ineffective if the path of the stirrer does not cause the necessary motion within the liquid composition. It is most desirable if the stirrer can impart motion to the liquid so that the liquid moves in a vertical direction and at the same time in a horizontal direction.
In attempting to achieve such motion, oscillating stirrers normally are of a type which can be referred to as "plungers," that is, the stirrer is moved up and down in a generally vertical plane. The stirrer frequently has some device attached at or near the end portion in the liquid to impart motion to the liquid.
U.S. Pat. No. 3,484,204 discloses such a stirrer driven by application of alternating positive and negative pressures to the interior of a reactor vessel containing a vertically moving rod having an enlargement on the lower end. U.S. Pat. No. 2,702,693 discloses use of a vertically moving stirrer having two pivotally mounted spring-biased arms with paddles in their end portions. Generally speaking, the motion of the liquid, when agitated by the above devices, will be in the same arcuate path in the vertical plane. In some instances the stirrer actuator will impart heat to the liquid which may be undesirable, particularly in laboratory work.
Another development to improve liquid flow was the magnetic stirrer, consisting of a bar magnet which is at the bottom of the vessel containing the liquid to be stirred and which is rotated by an external rotating magnetic field. This has become one of the preferred methods of light duty stirring. It has three disadvantages. The motor, which produces the external rotating magnetic field by rotating a permanent magnet, generates uncontrolled heat. Stirring ceases if the liquid is removed from the vicinity of the rotating magnetic field. If controlled heating is required it is necessary to use a specially designed electric hot plate or heating mantle which incorporates the motor. It is impossible to use a bunsen burner or a regulator electric hot plate. These three disadvantages are not usually serious in general laboratory practice but in the technique of spin culture of tissues and cells they cause complications and expense. Even though it is possible to insulate the passage of heat from the stirrer motor to the vessel, it is impossible to put the stirrer and vessel in a bench type incubator because the heat transferred to the air in the incubator will cause the temperature to rise above 37.degree.C. Either one must add a refrigerator to the incubator or work in a constant temperature room. An additional complication in tissue culture stirring is that the bar magnet must be kept off the bottom of the vessel, otherwise the cells will be damaged.
To overcome the disadvantages of the electrically actuated stirrers of the prior art as exemplified in the foregoing, my co-pending U.S. patent application Ser. No. 491,832 discloses the use of low pressure alternating current air, which shall be referred to as ACA throughout the remainder of this application. The ACA is delivered through a rubber stopper for the liquid container to the underside of which stopper there is cemented a rubber diaphragm seal having a flexible horizontal surface which is spaced from the underside of the stopper. A stirrer in the form of a glass or stainless steel rod is pushed into a tabulation at the center of the underside of the horizontal surface of the diaphragm. A horizontal perforated disc is attached to the lower end of the stirrer. The vertical oscillation of the stirrer imposed by the action of ACA against the diphragm generates stirring action and imparts movement to the liquid in the form of a torus which is continuously being turned inside out. The container is kept vertical for best results.
To improve the stirring action so as to impart motion to the liquid to cause it to move in X, Y and Z planes in an orbital path as occurs more closely in manual stirring, a known device discloses the use of a container closure which has two abutments of differing lengths depending from a disc through which ACA passes to strike a diaphragm held in place on the container by its closure. The diaphragm is a horizontal stiff disc with a stirrer depending from its underside. The ACA causes flexing of the stiff disc which is given a nutating motion by repeatedly striking the abutments of differing length. This nutating motion of the disc generates an orbital type of motion of the stirrer in the X, Y and Z planes of the liquid. The stirring of the liquid is improved over that of U.S. patent application Ser. No. 491,832. However, the diaphragm wears out rapidly as a result of striking the abutments. Again, the container must be kept vertical for best results.
The oscillatory stirring apparatus in my co-pending U.S. patent application Ser. No. 458,846 is a marked improvement over the known apparatus in that a pair of novel abutment plates are secured to the inner surface of the diaphragm supporting the stirring rod and strike a metal disc inserted into the diaphragm. The abutment plates are of unequal length and height in accordance with the principles of their design as disclosed in this application. Use is made of single phase ACA to impart motion to the diaphragm and the result is that the stirring motion is in an inclined elliptical path lying in the X, Y and Z planes. The stirring apparatus in this application can be secured to the various types of closures for flasks or other containers, but the flasks should be kept vertical.
My co-pending U.S. patent application Ser. No. 545,140 discloses oscillatory stirring apparatus in which either 2-phase ACA or 3-phase ACA is applied to a stirring assembly to achieve an orbital stirring path in the horizontal X and Y planes. In this application the stirring rod extends above and below a suspension diaphragm which provides a seal for the stirring rod within the flask and which is sealably secured to one of the various types of closures for flasks or containers. The portion of the stirring extending above the diaphragm and outside the flask is caused to move in an orbital path by the action of 2 or 3 expansible chambers which are cyclically, in an alternating pattern, supplied with positive and negative low pressures of ACA. The orbital path of this upper portion of the stirring rod is in the horizontal X and Y planes and normally has a small lateral displacement in each of these planes. The resultant movement of the end of the stirring rod within the flask is a similar orbital path as the upper porion outside the flask but with a lateral displacement in the horizontal and Y planes greaer than that of the upper portion in accordance with the distance of the lower end of the stirring rod from its pivotal base in the diaphragm. This 2 and 3-phase ACA system is very effective in the stirring of liquids, particularly the more viscous liquids. The stirring assembly of this application will allow the flask to be placed at an angle to the vertical and yet achieve excellent agitation.